Sorry that I overlooked this post at first. You are absolutely correct. Lincoln had promised in his First Inaugural to protect and defend Federal property. That meant that flag had stay over Sumter. Davis could not fully realize his complete separation from the United States as long as "that flag was still there". It was about that flag.
A Copy of which, as a courtesy, I have posted below.
My Lords, and Gentlemen,
Nothing could have afforded Me so much Satisfaction as to have been able to inform you, at the Opening of this Session, that the Troubles, which have so long distracted My Colonies in North America, were at an End; and that My unhappy People, recovered from their Delusion, had delivered themselves from the Oppression of their Leaders, and returned to their Duty. But so daring and desperate is the Spirit of those Leaders, whose Object has always been Dominion and Power, that they have now openly renounced all Allegiance to the Crown, and all political Connection with this Country. They have rejected, with Circumstances of Indignity and Insult, the Means of Conciliation held out to them under the Authority of Our Commission: and have presumed to set up their rebellious Confederacies for Independent States. If their Treason be suffered to take Root, much Mischief must grow from it, to the Safety of My loyal Colonies, to the Commerce of My Kingdoms, and indeed to the present System of all Europe. One great Advantage, however, will be derived from the Object of the Rebels being openly avowed, and clearly understood. We shall have Unanimity at Home, founded in the general Conviction of the Justice and Necessity of Our Measures.
I am happy to Inform you, that, by the Blessing of Divine Providence on the good Conduct and Valour of My Officers and Forces by Sea and Land, and on the Zeal and Bravery of the Auxiliary Troops in My Service, Canada is recovered; and although, from unavoidable Delays, the Operations at New York could not begin before the Month of August, the Success in that Province has been so important as to give the strongest Hopes of the most decisive good Consequences. But, notwithstanding this fair Prospect, We must, at all Events, prepare for another Campaign.
I continue to receive Assurances of Amity from the several Courts of Europe; and am using My utmost Endeavours to conciliate unhappy Differences between Two neighbouring Powers; and I still hope, that all Misunderstandings may be removed, and Europe continue to enjoy the inestimable Blessings of Peace. I think nevertheless that, in the present Situation of Affairs, it is expedient that We should be in a respectable State of Defence at Home.
Gentlemen of the House of Commons, I will order the Estimates for the ensuing Year to be laid before you. It is [a] Matter of real Concern to Me, that the important Considerations which I have stated to you must necessarily be followed by great Expence: I doubt not, however, but that My faithful Commons will readily and chearfully grant Me such Supplies, as the Maintenance of the Honour of my Crown, the Vindication of the just Rights of Parliament, and the Publick Welfare shall be found to require.
My Lords, and Gentlemen, in this arduous Contest I can have no other Object but to promote the true Interests of all My Subjects. No people ever enjoyed more Happiness, or lived under a milder Government, than those now revolted Provinces: the Improvements in every Art, of which they boast, declare it: their Numbers, their Wealth, their Strength by Sea and Land, which they think sufficient to enable them to make Head against the whole Power of the Mother Country, are irrefragable Proofs of it. My Desire is to restore to them the Blessings of Law and Liberty, equally enjoyed by every British Subject, which they have fatally and desperately exchanged for all the Calamities of War, and the arbitrary Tyranny of their Chiefs.
:)